Phew! Its that time of the year again. It is the season when sea turtles come in very large numbers on the beaches of Odisha to nest. The nesting sites receive so many turtles at the same time that it turns into a turtle ‘party’ zone.. However, for people counting them, it is a backbreaking exercise. Before I delve further into my ramblings, I shall in my capacity explain to you this amazing phenomenon called ‘Arribada.’

NIght Night

Arribada is a Spanish word for ‘arrival’. This phenomenon was first recorded in Latin America so the Spanish word stuck. Apart from Odisha, Olive Ridleys nest in similar fashion in Costa Rica and Mexico. What triggers such behaviour and why turtles only select certain beaches remains a mystery but the Olive Ridleys continue to aggregate in huge numbers on these beaches during Arribada. Quite often, it’s just a scramble for space since the numbers only seem to congregate in a select patch of the beach. In Rushikulya this year the beach had ‘grown’ in size due to constant shifting of sands and the area for these turtles was massive. Still as per our records, we could only find a handful of stretches full of turtles on them. Again, a wonder!

The entire process is actually quite daunting for the female. The male Olive Ridley turtles never come on land. On the contrary, females are known to nest all along the coast of India. So the nesting event can be primarily divided into sporadic nesters and mass nesters. You call an event mass nesting when you find 100 or more turtles nesting simultaneously on the beach. But it is a spectacle to see. As soon as the moon sets and the night is pitch dark (or close to it) you find these turtles coming out of the water towards the land to lay eggs.

They act as pre-programmed machines whose only job is to deliver the eggs in the nest and leave. Nothing else fazes them at this point in time.

Nesting Female

So how do you know how many have arrived? Simple! You only count the females that are actually laying eggs. The position in which a female is laying eggs is quite lucid. You can see her two hind flippers sticking out of the carapace and her body is almost at a 45-degree angle. If you dig a hole in between the carapace and the sand below, you can actually see the eggs being laid. One other thing that’s being recorded is ‘Ovipositing duration or OPD’- time taken to lay the eggs, number of eggs laid and after she is done, Curved Carapace Length (CCL) and Curved Carapace Width (CCW) is recorded. All these data are needed to better understand the populations that visit these beaches every year.

Turtles and crows

Counting only nesting females is reliable because females lay eggs only once in two years. So an overestimate or an underestimate of nesting turtles can be avoided. This makes life easier for everybody. This year though, Arribada lasted for only 2 nights. Not unusual as the same happened in 2007 as well. Maybe there is a pattern, maybe there is not, but the Arribada would continue to be one of nature’s greatest mysteries and Ridley’s greatest riddle!

Chetan Rao is currently working as a Research Associate with Dakshin Foundation, an organization based in Bangalore, on their long term project of monitoring of mas nesting rookery in Rushikulya beach in Orissa. He is a former alumnus of the Wildlife Institute of India, where he did his Master’s from in 2011. He is interested in biogeography and evolutionary biology of reptiles.